Sheet feeding device, and document feeding device in image reading apparatus comprising the same

ABSTRACT

A sheet feeding device, and a document feeding device including the sheet feeding device have a pickup roller which can elevate and lower between an operative position and a standby position, a sheet feeding rotating device that separably feeds each sheet from the roller, and a registration roller that registers the sheet from the sheet feeding rotating device. A carry-in roller conveys the sheet to a predetermined processing position, and a carry-out roller carries the sheet from the processing position. The pickup roller and sheet feeding rotating device are drivingly coupled to a first driving motor. The registration roller and carry-in roller are coupled to a second driving motor via a sliding friction clutch. The sliding friction clutch is configured so that the registration roller is rotated by rotating the second driving motor and transmission of a driving force is blocked by rotating the first driving motor.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to sheet feeding devices that feed sheetsto image forming apparatuses and various other instruments, andparticularly, to improvements in a driving mechanism and its controlmechanism for a document feeding device in an image reading apparatus.

Sheet feeding devices of this kind are commonly used in variousinstruments including image forming apparatuses such as copiers as wellas scanner apparatuses, as sheet feeding mechanisms that sequentiallydeliver sheets housed in a stacker or feeder mechanisms, or sequentiallyfeed sheets downstream which have been conveyed to a sheet guide or thelike. These mechanisms comprise rotating members (hereinafter referredto as roller means) such as rollers or belts which feed sheets set in asheet feeding stacker, downstream under a frictional force. In thiscase, a mechanism is also commonly used which, when the roller meansfeeds a sheet downstream, elevates and lowers the roller means between aposition where the roller means contacts the sheet and a position wherethe roller means is separate from the sheet, in accordance with sheetfeeding timing.

For example, according to Japanese Patent Laid-Open No. 10-338391,sheets placed on a sheet feeding tray are delivered by a pickup rollerlocated above the tray, and a sheet feeding roller located at the tip ofthe tray separates a sheet from the others. The leading end of the sheetabuts against a registration roller for registration located at adownstream side. The sheet is then fed to a downstream reading section.The pickup roller, sheet feeding roller, and registration roller arecoupled to the same driving motor. The driving motor rotates forward todrivingly move the pickup roller from a standby position located aboveto a delivery position on the tray, while rotating both rollers in thesheet feeding direction. The driving motor rotates backward to cause theregistration roller to feed the sheet from the sheet feeding rollerdownstream. Thus, forward and backward rotations of the single motorallow the pickup and sheet feeding roller and the registration roller tobe drivingly rotated in the opposite directions.

Japanese Patent Laid-Open No. 2002-182437 discloses a device having asheet feeding tray and a sheet discharging tray both located above areading platen and juxtaposed in a vertical direction, and a sheet fromthe sheet feeding tray is conveyed to the sheet feeding tray along aU-shaped conveying path via the reading platen. According to thisdocument, a pickup roller, a sheet feeding roller, and a registrationroller are coupled to a sheet feeding section motor as described above.A carry-in roller and a carry-out roller arranged upstream anddownstream, respectively, of the reading platen are coupled to aconveying section motor different from the sheet feeding section motor.This configuration allows a pickup operation and a registrationoperation to be timely performed by switching the rotation of the singlemotor between a forward direction and a backward direction. This deviceis thus made by enabling a driving mechanism to be simply constructedwithout using any special control parts such as an electromagneticclutch.

When a pickup operation and a registration operation are performed byswitching the rotation of the single motor between the forward andbackward directions as described above, the driving mechanism issimplified but the pickup roller repeats moving up and down whenever asheet is delivered. Thus, disadvantageously, a whack noise may be madewhen the pickup roller beats the upper surface of the sheet, and uponcontact with the sheet, the roller may beat only one side of the sheet,which may thus be wrinkled or skewed. Further, the sheet from which theimage is being read may be vibrated, resulting in a blurred image. Tosolve these problems, attempts have been made to elevate and lower thepickup roller using an independent motor or a solenoid. However, thishas increased the size and cost of the apparatus.

Thus, an object of the present invention is to provide a sheet feedingdevice that can perform a pickup operation and a registration operationusing a simple driving mechanism that can be easily controlled, whereinthe pickup operation involves elevating and lowering roller means fordelivering sheets from a stacker or the like, between an operativeposition and a retracted position.

Another object of the present invention is to provide a document feedingdevice that minimizes possible vibration, noise, skewing, and the likeduring sheet delivery when each of the sheets in a sheet feeding stackeris separably fed to a predetermined reading position.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

The present invention employs a configuration described below in orderto accomplish the above objects. In the present invention, the term“forward direction” of a first driving motor and a second driving motorrefers to a direction in which a sheet moves from a sheet feeding trayto a predetermined processing position (first platen) and a direction inwhich the sheet moves from the processing position to a sheetdischarging tray. The term “backward direction” refers to a direction inwhich the sheet moves in a direction opposite to the forward direction.Sliding friction clutch means refers to a friction clutch configured toslip at least a predetermined torque to prevent transmission of adriving force.

The present invention thus has pickup roller means located above aplacement tray on which sheets are placed, the pickup roller means beingable to elevate and lower between an operative position where the pickuproller means engages the sheets and a standby position located above theoperative position, sheet feeding rotating means for separably feedingeach sheet from the pickup means, and a registration roller thatregisters the sheet from the sheet feeding rotating means. A carry-inroller and a carry-out roller are arranged downstream of theregistration roller, wherein the carry-in roller conveys the sheet to apredetermined processing position, and the carry-out roller carries thesheet out from the processing position. The pickup roller means and thesheet feeding rotating means are drivingly coupled to the first drivingmotor. The registration roller and the carry-in roller are coupled tothe second driving motor.

The registration roller and the second driving motor are configured sothat the second driving motor transmits a driving force to theregistration roller via sliding friction clutch means. The slidingfunction clutch means is coupled to the registration roller so that theregistration roller is rotated by rotating the second driving motor andso that the transmission of a driving force to the registration rolleris blocked by rotating the first driving motor. In this case, forexample, the sliding friction clutch means has a rotating shaftconnected to the registration roller and around which a coil spring iswound so that rotation of the second driving motor is transmitted to therotating shaft via the coil spring, while the transmission is cancelledby rotating the first driving motor, coupled to the coil spring, in apredetermined direction. More specifically, the coil spring is woundaround the rotating shaft so that the spring can be compressed andloosened. The second and first driving motors are coupled to the coilspring so as to exert a rotating force in a direction in which the coilspring is compressed and in a direction in which the coil spring isloosened, respectively. The transmission of driving from the seconddriving motor to the rotating shaft is turned on and off on the basis ofthe difference in rotation speed between the first driving motor and thesecond driving motor.

A document feeding device in an image reading apparatus in accordancewith the present invention comprises a placement tray on which sheetsare placed, a sheet feeding path along which a sheet from the placementtray is guided to a reading position, a sheet discharging path alongwhich the sheet from the reading position is guided to a sheetdischarging tray, pickup roller means located above the placement trayand configured to elevate and lower freely between an operative positionwhere the pickup roller means engages the sheet and a standby positionlocated above the operative position, sheet feeding rotating means forseparably feeding each sheet from the pickup roller means, aregistration roller located on the sheet feeding path to register thesheet from the sheet feeding rotating means and a carry-in roller thatconveys the sheet from the registration roller to the reading position,a carry-out roller located on the sheet discharging path to carry thesheet out from the reading position and a sheet discharging roller thatcarries the sheet from the carry-out roller out to the sheet dischargingtray, a first driving motor that is able to rotate forward and backwardto drivingly rotate the pickup roller means and the sheet feedingrotating means, and a second driving motor that is able to rotateforward and backward to drivingly rotate the registration roller,carry-in roller, carry-out roller, and sheet discharging roller.

The pickup roller means and sheet feeding rotating means are coupled tothe first driving motor so as to be drivingly rotated in a sheet feedingdirection by rotating the first driving motor forward. The pickup rollermeans is coupled to the first driving motor so as to be moved from thestandby position to the operative position by rotating the first drivingmotor forward and to be moved from the operative position to the standbyposition by rotating the first driving motor backward. The registrationroller, carry-in roller, carry-out roller, and sheet discharging rollerare coupled to the second discharging motor so as to be drivinglyrotated in the sheet feeding direction by rotating the second drivingmotor forward. The second driving motor transmits a driving force to theregistration roller via sliding friction clutch means. The slidingfriction clutch means is configured so that transmission of a drivingforce from the second driving motor to the registration roller isblocked by rotating the first driving motor forward.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an entire document feeding devicecontaining a sheet feeding device in accordance with the presentinvention;

FIG. 2 is an enlarged diagram illustrating an essential part of thedevice in FIG. 1;

FIG. 3 is a diagram illustrating a driving transmitting mechanism for asheet feeding motor in the device in FIG. 1;

FIG. 4 is a diagram illustrating a driving transmitting mechanism for aconveying motor in the device in FIG. 1;

FIG. 5 is a diagram illustrating essential parts of the drivingtransmitting mechanisms in FIGS. 3 and 4;

FIG. 6 is an exploded perspective view showing a driving transmittingmechanism for a registration roller in FIG. 5;

FIG. 7( a) is a sectional view of an essential part of the drivingtransmitting mechanism for the registration roller in FIG. 5, and FIG.7( b) is a sectional view of an essential part of the drivingtransmitting mechanism for the registration roller in FIG. 5; and

FIG. 8 is a timing chart showing the control of the motors in FIGS. 3and 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the drawings, description will be given below for asheet feeding device and an image reading apparatus comprising the sheetfeeding device. FIG. 1 is a diagram showing the general configuration ofa document feeding device incorporated in an image reading apparatussuch as a scanner or a copier. FIG. 2 is a diagram illustrating anessential part of a sheet feeding section of the document feedingdevice. FIG. 3 is a diagram illustrating a driving mechanism in thedevice in FIG. 2. First, with reference to FIGS. 1 and 2, descriptionwill be given for the configuration of the document feeding device inthe image reading apparatus and then the sheet feeding device inaccordance with the present invention.

In FIG. 1, reference numeral 10 denotes a document feeding device(hereinafter referred to as an “ADF”) incorporated into an image readingapparatus. The ADF 10 includes a U-shaped conveying path (a sheetfeeding path 25 and a carry-out path 26 described below) along which asheet is conveyed so as to pass over a top surface of a first platen 2provided in the image reading apparatus 1. The image reading apparatus 1has a light source 3 such as a lamp which is located below the firstplaten 2, a mirror 4 that polarizes reflected light resulting fromirradiation of a sheet with light from the light source 3, and opticalreading means (not shown) such as a CCD sensor (charge coupled device)which electrically reads an image from the sheet. The image readingapparatus 1 has a reading section provided on the top surface of thefirst platen 2. The image reading apparatus 1 includes a second platen 5on which a sheet is stationarily set. The ADF 10, located above thesecond platen 5, is opened, and a light source unit (carriage) composedof the light source 3, the mirror 4, and the like is moved in asub-scanning direction to read a sheet image from a book document orother sheets set on the second platen 5.

The ADF 10 includes a placement tray 15 on which a plurality of sheetsare placed, a sheet feeding section 11 that separably feeds each of thesheets on the placement tray 15 toward the first platen 2, a conveyingsection 12 that passes the sheet along the top surface of the firstplaten 2 at a predetermined speed, a sheet discharging section 13 thatreceives and discharges the sheet having passed over the top surface ofthe first platen 2, and a sheet discharging tray 16 that houses thesheet from the sheet discharging section 13. The ADF 10 further includesa switchback section 14 that allows the sheet discharging section 13 toswitch back the sheet carried out from the first platen 2 to return thesheet to the sheet feeding section 11 so that the first platen 2 canread a back surface of the sheet. The ADF 10 further includes acirculating path 30.

The sheet feeding section 11 is composed of the above placement tray 15,a pickup roller 18, sheet feeding rotating means 19, a registrationroller 21, and a sheet feeding path 25. The placement tray 15 iscomposed of a tray member shaped so that sheets with a size preset inaccordance with apparatus specifications are placed. Side guides 17 arelocated on the placement tray 15 so that the side edges of a sheet canbe aligned with the side guides 17. A gate stopper 38 is located at aleading end of the placement tray 15 so that the leading end of a sheetcan be abutted against and aligned with the gate stopper 38; the gatestopper 38 can be projected from and retracted onto the placement tray15. The illustrated placement tray 15 is attached to a device frame soas to incline at a predetermined angle. The placement tray 15 can pivotaround a supporting point at its leading end, shown at 15 a in thefigure.

The pickup roller 18 is located so as to be able to elevate and lowerbetween a standby position (corresponding to the state shown in FIG. 2)located above the placement tray 15 and an operative position in whichthe pickup roller 18 engages the sheets on the tray. An elevating andlowering arm 18 a is supported by a rotating support shaft 19 b attachedto the device frame, so as to be able to swing freely. The elevating andlowering arm 18 a has the pickup roller 18 supported at its leading end.A first driving motor M1 described below is coupled to the rotatingsupport shaft 19 b to transmit its rotation to the pickup roller 18.

The sheet feeding rotating means 19 is composed of rotating members suchas a belt and a roller in order to separably feed each sheet downstream;the illustrated sheet feeding rotating means 19 is composed of a sheetfeeding roller supported by the rotating support shaft 19 b. In thedescription below, the sheet feeding rotating means is the sheet feedingroller 19. Separating means 20 such as a separating pad (not shown) or aseparating roller is brought into pressure contact with the sheetfeeding roller 19 to separably feed each sheet delivered by the pickuproller 18, to the interior of the apparatus. The arrangement of thesheet feeding roller 19 will be described below. Since sheets are set inthe placement tray 15 by centering, the sheet feeding roller 19 islocated at a position corresponding to the center of the sheets.

The sheet feeding path 25 is curved like the letter U to guide a sheetfrom the placement tray 15 to a processing position (first platen 2described above). The registration roller 21 is located on the sheetfeeding path 25 and composed of a pair of rollers 21 a and 21 b that arein pressure contact with each other. One of the rollers 21 a and 21 b iscoupled to a second driving motor M2 described below. The conveyingsection 12 is composed of a carry-in roller 22 located upstream of thefirst platen 2 and a carry-out roller 23 located downstream of the firstplaten 2. Each of these rollers 22 and 23 is composed of a pair ofrollers that conveys a sheet nipped between them. A backup guide 26 a islocated above the first platen 2, and a scooping guide 6 is locateddownstream of the first platen 2. Reference numeral 26 in the figuredenotes a conveying path along which a sheet from the first platen 2 iscarried out and guided to a sheet discharging path described below 27.

The sheet discharging section 13 is composed of a sheet discharging path27, a path switching flapper 29 located on the sheet discharging path27, and a sheet discharging roller 24. A rear end of the sheetdischarging path 27 constitutes a switchback path 28. The switchbackpath 28 continues into a circulating path 30. The sheet dischargingroller 24 rotates reversely with the trailing end of a sheet nippedbetween the rollers to switch back and feed the sheet to the circulatingpath 30. Thus, a sheet discharging roller 24 b is separated from a sheetdischarging roller 24 a when the end of a sheet passes by the rollers;the sheet discharging rollers 24 a and 24 b constitute the sheetdischarging roller 24. Further, the path switching flapper 29 is alwaysurged downward by an urging spring to switch the path by means of anelectromagnetic solenoid.

The circulating path 30 is composed of an upper guide 28 a and a lowerguide 28 b so as to guide the sheet having its conveying directionreversed by the switchback path 28. Reference numeral 28 in the figuredenotes a Myler guide that guides the sheet from the circulating path 30to a nip point of the registration roller 21. A plurality of sensors S1,S2, and S3 (FIG. 1) is located on the placement tray 15 to detect asheet size. The placement tray 15 has an empty sensor S4 that detectsthe presence or absence of a sheet. The sheet feeding path 25 has aregistration sensor S5 that detects the leading and trailing ends of aconveyed sheet. A lead sensor S6 is provided upstream of the firstplaten 2 to detect the leading end of the sheet. The carry-out path 26has a carry-out sensor S7. The sheet discharging path 27 has a sheetdischarging sensor S8. The sensors S1 to S8 are connected to a CPU thatdrivingly controls the whole device. On the basis of detection signalsfrom the sensors, the driving motors M1 and M2 and electromagneticsolenoid, described below, are controlled.

In the present invention, the pickup roller 18, sheet feeding roller 19,registration roller 21, carry-in roller 22, carry-out roller 23, andsheet discharging roller 24 are coupled to the first and second drivingmotors. Driving mechanisms for the conveying rollers will be describedwith reference to FIGS. 3 and 4.

FIG. 3 shows a driving mechanism for the first driving motor M1(hereinafter referred to as a sheet feeding motor) that drivinglyrotates the pickup roller 18 and sheet feeding roller 19. The sheetfeeding motor M1 can rotate forward and backward to drivingly rotate thepickup roller 18 and sheet feeding roller in the sheet feedingdirection. Moreover, the sheet feeding motor M1 swings the elevating andlowering arm 18 a in a vertical direction, which supports the pickuproller 18. Thus, the sheet feeding motor M1 is coupled to the rotatingsupport shaft 19 b via a pulley P16, a timing belt T16, a pulley P36, agear Z17, a gear 19, and a gear 18. Consequently, the rotating supportshaft 19 b rotates forward and backward in conjunction with the sheetfeeding motor M1. Rotation of the sheet feeding roller 19 is transmittedto the rotating support shaft 19 b via a one-way clutch OW2 and then tothe pickup roller 18 via the timing belt T2. The one-way clutch OW2transmits only the forward rotation of the sheet feeding motor M1 to thepickup roller 18 and sheet feeding roller 19, which thus rotate in thesheet feeding direction.

On the other hand, a base end of the elevating and lowering arm 18 a isfitted around the rotating support shaft 19 b via spring clutches A andB. The spring clutches are set so as to be loosened when the rotatingsupport shaft 19 b rotates forward and so to be compressed when therotating support shaft 19 b rotates backward. Consequently, forwardrotation of the rotating support shaft 19 b loosens the spring clutchesto swing the elevating and lowering arm 18 a from the standby position,located above, to the operative position, located below, under its ownweight. In contrast, backward rotation of the rotating support shaft 19b compresses the spring clutches to raise the elevating and lowering arm18 a from the operative position to the standby position under arotating torque from the shaft. Although not shown, the elevating andlowering arm 18 a has a stopper at its standby position. While beingrestricted by the stopper, the elevating and lowering arm 18 a is heldat the standby position through the action of a spring clutch C (torquelimiter) located between the pulley P36 and the gear Z17.

Even after the sheet feeding motor M1 is stopped, the spring clutches Aand B remain compressed to hold the elevating and lowering arm 18 a atthe standby position under the load of the driving system. Thus, forwardrotation of the sheet feeding motor M1 lowers the pickup roller 18 fromthe standby position to the operative position. The pickup roller 18then rotates in the sheet feeding direction to deliver the sheets on theplacement tray 15 in conjunction with the sheet feeding roller 19. Afterall the sheets on the placement tray 15 are delivered, the sheet feedingmotor M1 rotates backward to swing the elevating and lowering arm 18 ato raise the pickup roller 18 from the operative position to the standbyposition. In FIG. 3, the driving force of the sheet feeding motor M1 istransmitted from a gear 61 to a gear 66. The action of the driving forcewill be described below.

Now, description will be given to a driving mechanism for the seconddriving motor (hereinafter referred to as the conveying motor) M2, whichdrivingly rotates the registration roller 21, carry-in roller 22,carry-out roller 23, and sheet discharging roller 24; the drivingmechanism is shown in FIG. 4. The driving motor M2 can rotate forwardand backward and is coupled to a driving roller 22 a of the carry-inroller 22 through a pulley P31 via a pulley P26, a timing belt T4, apulley P46, a pulley P33, and a timing belt T6. Similarly, the drivingmotor M2 is coupled to a driving roller 23 a of the carry-out roller 23through a pulley P32. A driving force is also transmitted to pinchingrollers 22 b and 23 b that are in pressure contact with the aboverollers; a driving force is transmitted to the pinching roller 22 b viagears Z3 and Z4 and to the pinching roller 23 b via gears Z1 and Z2.Illustrated spring clutches C and D serve as torque limiters that absorbthe difference in peripheral speed.

On the other hand, the driving force of the conveying motor M2 istransmitted to the sheet discharging roller 24 through a pulley 42, atiming belt T5, and a pulley P48 shown in FIG. 4. The driving force isalso transmitted to a driving roller 24 a of the sheet dischargingroller 24 via a spring clutch E and to a pinching roller 24 b throughgears Z5 and Z6. The peripheral speed of the driving roller 24 a is setslightly higher than that of the pinching roller 24 b. When one sheet isnipped or no sheet is present, the spring clutch E allows the drivingroller 24 a to follow the peripheral speed of the pinching roller 24 b.The peripheral speed of the pinching roller 24 b is set to the same asthat of the driving roller 23 a of the carry-out roller 23. Moreover,the sheet discharging roller 24 has an electromagnetic solenoid (notshown) that separates the driving roller 24 a from the pinching roller24 b. The driving roller 24 a is provided with a coaxial reversepreventing lever 35 via a spring clutch F.

Thus, rotation of the conveying motor M2 is transmitted to a timing beltT3 through the timing belt T5 via a pulley 63 and a pulley 67 that iscoaxial with the pulley 63. The rotation is further transmitted to adriving roller 21 a of the registration roller 21 via a one-way clutchOW1 provided on the pulley 28 a. This transmission system has a slidingfriction clutch means 60 described below. The sliding friction clutchmeans 60 is configured as shown in FIGS. 5 and 8 to transmit rotation ofthe conveying motor M2 to the registration roller 21 and to block thetransmission of the driving force (turn off the driving operation) whenthe sheet feeding motor M1 is drivingly rotating under predeterminedconditions.

As shown in FIGS. 4 and 5, the timing belt T 5 for the conveying motorM2 is coupled through the pulley 63 to a rotating shaft 62 thatcontinues into the registration roller 21 (in the figure, via the timingbelt T3). The pulley 63 is loosely fitted around the rotating shaft 62so as to avoid the direct transmission of a driving force from therotating shaft 62. As shown in FIG. 7( a), a coil spring 65 is woundbetween a driving sleeve 63 a integrated with the pulley 63 and a drivensleeve 64 fixed to the rotating shaft 62. The driving sleeve 63 a isloosely fitted around the rotating shaft 62, and the driven sleeve 64 isfixed to the rotating shaft 62. The driving and driven sleeves 63 a and64 have substantially the same diameter. A spring 65 is wound around thedriving and driven sleeves 63 a and 64. The spring 65 is set on theloosening side when the pulley 63 rotates clockwise (CW) in FIG. 6 andon the compressing side when the pulley 63 rotates counterclockwise(CCW) in FIG. 6. The CCW rotation of the pulley 63 is transmitted to thedriving shaft 62 via the driven sleeve 64.

On the other hand, a driven sleeve-side end of the spring 65 is bent andfixed to the gear 66. The gear 66 is loosely fitted on and supported byflanges formed on the driving sleeve 63 a and driven sleeve 64 so as torotate freely regardless of rotation of the pulley 63 and rotating shaft62. The gear 61, connected to the sheet feeding motor M1, meshes withthe gear 66. The gear 61 is attached to the rotating shaft 61 a (seeFIG. 3) via the one-way clutch OW to transmit the rotation of the sheetfeeding motor M1 to the rotating shaft 61 a through the pulley P36 andtiming belt T16. The one-way clutch OW is set so as to avoidtransmitting forward rotation (CCW in FIG. 3) of the driving sleeve 63 ato the rotating shaft 61 a as shown in FIG. 7( b).

Now, the operation of the driving mechanism will be described withreference to the timing chart shown in FIG. 8.

“Leading Sheet (First Sheet) Feeding Operation (First Operation)”

The apparatus is powered on to turn on the empty sensor S4 on theplacement tray 15 to rotate the sheet feeding motor M1 forward (sheetfeeding direction). At this time, the conveying motor M2 is stopped. Theforward rotation of the sheet feeding motor M1 rotates the pickup roller18 and the sheet feeding roller 19 in the sheet feeding direction(rightward in the figure). At the same time, the spring clutches A and Bbetween the rotating support shaft 19 b and the elevating and loweringarm 18 a holding the pickup roller 18 are compressed to swing theelevating and lowering arm 18 a in conjunction with rotation of therotating support shaft 19 b to lower the elevating and lowering arm 18 afrom the standby position to the operative position. The rotation of therotating support shaft 19 b is similarly transmitted, via the timingbelt T2, to the pickup roller 18 supported at a swinging end of theelevating and lowering arm 18 a. The rotating operation of the pickuproller 18 delivers each of the sheets on the placement tray 15 to thesheet feeding roller 19. The separating means 20 then separably feedsthe delivered sheet. The elevating and lowering arm 18 a stops swingingwhen the pickup roller 18 moves to the operative position to press theleading sheet to loosen the spring clutches A and B to stop rotating therotating support shaft 19 b. Further, the elevating and lowering arm 18a moves to the standby position to abut against a stopper (not shown) toloosen the spring clutch C. This turns off the sheet feeding drivingsystem.

This operation allows the leading end of the sheet carried out to thesheet feeding path 25 to be sensed by the registration sensor S5.Subsequently, the sheet abuts against the registration roller 21. Atthis time, the conveying motor M2 coupled to the registration roller 21is at a stop, so that the leading end of the sheet abuts against the nippoint of the registration roller 21 and is thus bent. The bending of thesheet allows the leading end of the sheet to be registered. At apredetermined delay time (registration time) after the issuance of asensing signal from the registration sensor S5, the sheet feeding motorM1 is stopped. During this process, in the sliding friction clutch means60, the gear 66 rotates in conjunction with the gear 61 coupled to thesheet feeding motor M1. However, since the spring 65 is set in anopening direction (loosening direction), the spring 65 and the drivensleeve 64 slip against each other to keep the rotating shaft 62 at astop; the rotating shaft 62 is not driven by the sheet feeding motor M1.The registration roller is at a stop without being rotated.

“Conveyance by the Registration Roller (Second Operation)”

Then, a predetermined time after a processing operation such as imagereading, a sheet feeding instruction signal is issued, and in responseto the signal, the conveying motor M2 is rotated forward (sheet feedingdirection). At this time, the sheet feeding motor M1 is at a stop aspreviously described. The forward rotation of the conveying motor M2rotates the pulley 63 clockwise in FIG. 5 to compress the coil spring 65wound around the driving sleeve 63 a. The driven sleeve 64 is thusrotated clockwise in FIG. 6 to rotate the rotating shaft 62 in the samedirection. Rotating the rotating shaft clockwise in FIG. 6 rotates theregistration roller 21 coupled to the rotating shaft 62 in the sheetfeeding direction.

The rotation of the registration roller 21 transfers the sheetdownstream along the sheet feeding path 25. Simultaneously with theoperation of the registration roller 21, the forward rotation of theconveying motor M2 is transmitted to the carry-in roller 22 andcarry-out roller 23 via the pulley P33 and timing belts T6 and T7 aspreviously described. These rollers are thus rotated in the sheetfeeding direction. The motor M2 also transmits rotation in a sheetdischarging direction to the sheet discharging roller 24 via the timingbelt T5 and pulley P48. During this process, the clockwise rotation (inFIG. 5) of the gear 61 meshed with the gear 66 of the rotating shaft 62is not transmitted to the sheet feeding motor M1 by the built-in one-wayclutch OW.

“Stopping the Registration Roller (Third Operation)”

The lead sensor S6, located upstream of the carry-in roller 22, sensesthe leading end of the sheet conveyed as described above to issue a cuesignal in accordance with which the first platen 2 reads an image. Then,the registration sensor S5 senses the trailing end of the sheet, andafter the time when the trailing end of the sheet is expected to passthrough the registration sensor 21, the sheet feeding motor M1 at a stopis actuated to rotate forward (sheet feeding direction). At this time,the conveying motor M2 continuously rotates forward (sheet feedingdirection). Rotating the sheet feeding motor M1 and the conveying motorM2 at the same time subjects the coil spring 65 around the rotatingshaft 62 to both the rotating force of the conveying motor in acompressing direction (shown by arrow a in FIG. 7( b)) and the rotatingforce of the sheet feeding motor M1 in a loosening direction (shown byarrow b).

Thus, for the sliding friction clutch means 60, the relationship betweenthe rotation speed V2 (angular speed) of the conveying motor M2transmitted to the rotating shaft 62 by the pulley 63 and the rotationspeed V1 (angular speed) of the sheet feeding motor M1 transmitted bythe gear 66 is set to be V1>V2. That is, the rotation speed of the sheetfeeding motor M1 in the loosening direction acts more significantly onthe coil spring 65 than the rotation speed of the conveying motor M2 inthe compressing direction.

Consequently, the driving sleeve 63 a and the coil spring 65 slipagainst each other, preventing the driving force of the sheet feedingmotor M1 from being transmitted to the rotating shaft 61 a. This stopsthe registration roller 21. On the other hand, rotation of the conveyingmotor M2 is transmitted to the carry-in roller 22, carry-out roller 23,and sheet discharging roller 24, coupled to the conveying motor M2.These rollers continue to rotate in the above directions. Accordingly,the sheet conveyed by the registration roller has its trailing endcarried out from the roller 21 and is then conveyed to the first platen2 by the carry-in roller 22. The platen then executes a reading process.The sheet from the platen 2 is carried out to the sheet discharging tray16 by the carry-out roller 23 and sheet discharging roller 24.

“Delivering and Conveying the Second Sheet (Fourth Operation)”

The simultaneous rotation of the sheet feeding motor M1 (forwardrotating CW direction) and conveying motor M2 (forward rotating CCWdirection) stop the registration roller 21 as described above. At thesame time, the pickup roller 18 and sheet feeding roller 19, coupled tothe sheet feeding motor M1, rotate in the sheet feeding direction todeliver the next sheet from the placement tray 15 for registration. Onthe basis of the timing when the next sheet is fed to the registrationroller 21, for example, on the basis of a leading end sensing signalfrom the registration sensor S5, the sheet feeding motor M1 is stopped.The conveying motor M2 finishes carrying the sheet out to the sheetdischarging tray 16 and stops before the sheet feeding motor M1 stops.Further, stopping and rotating the registration roller 21 does notnecessarily require the stoppage of the conveying motor M2; theregistration-roller 21 can be stopped and rotated with the conveyingmotor M2 rotating, by rotating and stopping the sheet feeding motor M1.Then, in this state, the sheet fed to the registration roller 21 waitsfor the next sheet feeding instruction signal. Subsequently, the processreturns to the second operation, which is then repeated as describedabove.

“Circularly Conveying Sheets (Fifth Operation)”

On the other hand, the sheet from which the image has been read is fedto the carry-out path 26 and carry-out path 27. At this time, in adouble-side reading mode in which the back surface of the sheet is alsoread, the carry-out sensor S7 detects the trailing end of the sheetduring above second operation. A predetermined time later, the carry-outsensor S7 switches the rotation of the conveying motor M2 to thebackward direction (CW direction). At this time, the sheet feeding motorM1 is kept at a stop. The backward rotation of the conveying motor M2reverses the direction in which the sheet nipped by the sheetdischarging roller 24 is conveyed. The sheet is then fed to thecirculation circuit 30. When the sheet is fed along the circulating path30 and the trailing end of the sheet reaches the registration roller 21,the registration roller 21 at a stop registers the leading end of thesheet. That is, the backward rotation (CW direction) of the conveyingmotor M2 is transmitted to the pulley 63. However, a rotating force inthe loosening direction acts on the coil spring 65 to prevent thebackward rotation from being transmitted to the rotating shaft 62,coupled to the registration roller 21. After the circulated sheet isregistered by the registration roller 21, the conveying motor receives asheet feeding instruction signal at a predetermined timing and is thusrotated forward (CCW direction). The process returns to the secondoperation, which is then sequentially repeated.

“Pickup Roller Returning Operation (Sixth Operation)”

Once all the sheets on the placement tray 15 are delivered, the emptysensor S4 is turned off to issue the corresponding signal. Then, whenthe final sheet is carried out to the sheet discharging tray 16, forexample, after a predetermined delay time since the sheet dischargingsensor S8 issues a sheet trailing end detection signal, the sheetfeeding motor M1 is rotated backward (CCW rotation). The rotationcompresses the spring clutches A and B, provided on the elevating andlowering arm 18 a as described above, to raise the elevating andlowering arm 18 a from the operative position to the standby positionunder the rotating torque from the support shaft. Even after the sheetfeeding motor M1 is stopped, the spring clutches A and B remaincompressed to hold the elevating and lowering arm 18 a in its standbyposition under the load of the driving system.

As described above, according to the present invention, the firstdriving motor drivingly rotates the pickup roller and sheet feedingrotating means, which separates and feeds each of the sheets on theplacement tray. The second driving motor drivingly rotates theregistration roller and carry-in roller, located downstream of thepickup roller and sheet feeding rotating means. Further, the slidingfriction clutch means is provided between the second driving motor andthe registration roller. The transmission of a driving force through thesliding friction clutch means is blocked by the corresponding rotationof the first driving motor. Consequently, even while a sheet deliveredfrom the tray is being conveyed by the downstream carry-in roller, therotation of the first driving motor for delivering the following sheetblocks the transmission of a driving force to the registration roller.This enables the pickup roller and sheet feeding rotating member todeliver the next sheet to the registration roller at a stop, allowingthe sheet with its leading end registered to stand by. Thus, sheets canbe consecutively fed at a high speed.

Therefore, compared to the conventional technique with which a motorrotates forward to perform a pickup operation and backward to perform aregistered feeding operation, the present invention can control themotor so that the pickup roller is lowered from the standby positionbefore starting the operation and raised from the operative positionafter finishing the operation. This eliminates the need to elevate andlower the pickup roller between the standby position and the operativeposition whenever a sheet is to be delivered. A precise process can beexecuted at the downstream processing position without any noise orvibration. Moreover, the required configuration is such that, forexample, the coil spring is wound around the rotating shaft, connectedto the registration roller, so that the registration roller beingrotated by the second driving motor can be stopped by appropriatelyrotating the first driving motor to loosen the coil spring. Thus, therequired structure is simple and can be easily controlled. Therefore,the present invention exerts significant effects.

Therefore, the automatic sheet feeding device set forth in the presentinvention can controllably stop and rotate the registration roller byrotating the sheet feeding motor forward and stopping it. The deviceenables the sheet to be separated from the pickup roller to stand by byreversely rotating the sheet feeding motor. This allows the provision ofan automatic sheet feeding device and an image processing apparatuswhich eliminate the need for an expensive electromagnetic clutchotherwise required to stop and rotate the registration roller, thedevice and apparatus also enabling the pickup roller to always abutagainst the sheet during the sequential separation and feeding ofsheets, reducing the possibility of vibration or noise.

Further, the sheet feeding motor M1 can be driven at a low speed whilethe registration roller 21 is being driven. By rotating the motor at adriving speed appropriate to prevent a plurality of overlapping sheetsfrom being simultaneously fed, it is possible to feed the sheet beingconveyed by the conveyance driving system, in a trailing end-firstposition. This enables smooth conveyance with a reduced conveying load.

The disclosure of Japanese Patent Application No. 2006-103668 filed onApr. 4, 2006, is incorporated as a reference.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

1. A sheet feeding device comprising: a placement tray on which sheetsare placed; pickup roller means configured to move up and down betweenan operative position where the pickup roller means engages a sheet anda standby position located above the operative position; sheet feedingrotating means for separably feeding each sheet from the pickup means; aregistration roller located downstream of the sheet feeding rotatingmeans to register the sheet from the sheet feeding rotating means; acarry-in roller located downstream of the sheet feeding rotating meansto transfer the sheet to a predetermined processing position; acarry-out roller for carrying the sheet out from the processingposition; a first driving motor for rotating the pickup roller means andthe sheet feeding rotating means; a second driving motor for rotatingthe registration roller and the carry-in roller; and sliding frictionclutch means situated between the second driving motor and theregistration roller, the sliding friction clutch means being coupled tothe registration roller so that the registration roller is drivinglyrotated by operating the second driving motor, and transmission of adriving force to the registration roller is blocked by operating of thefirst driving motor.
 2. The sheet feeding device according to claim 1,wherein the sliding friction clutch means comprises a rotating shaftconnected to the registration roller; and a coil spring wound around therotating shaft, and rotation of the second driving motor is frictionallytransmitted to the rotating shaft via the coil spring, and frictionaltransmission of rotation of the rotating shaft with the coil spring iscancelled by rotating the first driving motor in a predetermineddirection.
 3. The sheet feeding device according to claim 2, wherein thecoil spring is wound around the rotating shaft so as to be freelycompressed and loosened, the second driving motor and the first drivingmotor are coupled to the coil spring so as to rotate in a compressingdirection and in a loosening direction, respectively, and transmissionof a driving force from the second driving motor to the rotating shaftis controlled on a basis of a difference in rotation speed between thefirst driving motor and the second driving motor which act on the coilspring.
 4. The sheet feeding device according to claim 1, wherein thepickup roller means is attached to a swinging arm member supported by arotating support shaft, the rotating support shaft is coupled to thefirst driving motor, and the swinging arm member is coupled to therotating support shaft so that the pickup roller means is moved from thestandby position to the operative position by rotating the first drivingmotor forward and from the operative position to the standby position byrotating the first driving motor backward.
 5. The sheet feeding deviceaccording to claim 1, wherein the first driving motor is configured torotate forward and backward, the pickup roller means and the sheetfeeding rotating means are coupled together so as to be rotated byrotating the first driving motor forward, the pickup roller means iscoupled to the sheet feeding rotating means so as to be moved from thestandby position to the operative position by rotating the first drivingmotor forward and from the operative position to the standby position byrotating the first driving motor backward, and the sliding frictionclutch means is configured so that transmission of a driving force fromthe second driving motor to the registration roller is blocked byrotating the first driving motor forward.
 6. A document feeding devicein an image reading apparatus, comprising: a placement tray on whichsheets are placed; a sheet feeding path for guiding a sheet from theplacement tray to a reading position; a sheet discharging path forguiding the sheet from the reading position to a sheet discharging tray;pickup roller means located above the placement tray and configured tomove up and down between an operative position where the pickup rollermeans engages the sheet and a standby position located above theoperative position; sheet feeding rotating means for separably feedingeach sheet from the pickup roller means; a registration roller locatedon the sheet feeding path to register the sheet from the sheet feedingrotating means; a carry-in roller located on the sheet feeding path fortransferring the sheet from the registration roller to the readingposition; a carry-out roller located on the sheet discharging path tocarry the sheet out from the reading position; a sheet dischargingroller located on the sheet discharging path, for carrying the sheetfrom the carry-out roller out to the sheet discharging tray; a firstdriving motor configured to rotate forward and backward to drivinglyrotate the pickup roller means and the sheet feeding rotating means,wherein the pickup roller means and sheet feeding rotating means arecoupled to the first driving motor so as to be drivingly rotated in asheet feeding direction by rotating the first driving motor forward, andthe pickup roller means is coupled to the first driving motor so as tomove from the standby position to the operative position by rotating thefirst driving motor forward and to move from the operative position tothe standby position by rotating the first driving motor backward; asecond driving motor configured to rotate forward and backward todrivingly rotate the registration roller, carry-in roller, carry-outroller, and sheet discharging roller, wherein the registration roller,carry-in roller, carry-out roller, and sheet discharging roller arecoupled to the second discharging motor so as to drivingly rotate in thesheet feeding direction by rotating the second driving motor forward;and sliding friction clutch means situated between the second drivingmotor and the registration roller, for transmitting a driving force fromthe second driving motor to the registration roller, the slidingfriction clutch means being configured so that transmission of thedriving force from the second driving motor to the registration rolleris blocked by rotating the first driving motor forward.
 7. The documentfeeding device according to claim 6, wherein a circulation path forguiding the sheet from the sheet discharging roller to the sheet feedingpath is connected to the sheet discharging path, the sheet dischargingroller is coupled to the second driving motor so that the sheet iscarried out to the sheet discharging tray by rotating the second drivingmotor forward, and the sheet is reversed and conveyed to the circulationpath by rotating the second driving motor backward, and the registrationroller is coupled to the second driving motor via a one-way clutch so asto be drivingly rotated in the sheet feeding direction by rotating thesecond driving motor forward.